We propose to study the structure and function of the EcoRI and EcoRII restriction-modification systems in order to elucidate how proteins recognize specific DNA sequences. Strains producing higher levels of the enzymes will be constructed using recombinant DNA technology. Functional analysis will include measuring enzyme binding and reactions with a variety of natural and synthetic substrates. Primary structure of the enzymes will be determined by sequencing the genes. The chemical probes, dimethyl sulfate and nitrosourea, will be used to define gases and phosphate groups of DNA with which the proteins are in close contact. X-ray diffraction analysis of the system will be performed by John Rosenberg.